The present invention relates to a piezoelectric sensor and, more particularly, to an improvement in a piezoelectric sensor for use with a vortex flow meter.
There has been proposed and put to practical use a piezoelectric sensor of the type having a piezoelectric element sandwiched between conductive electrodes. When an external force is imparted to the sensor, the sensor senses a magnitude of the force by detecting a voltage which is generated by the deformation of the piezoelectric element originating from the external force.
A piezoelectric sensor of the type described is rarely used naked or exposed to the outside and usually is embedded in a detector member or cassette through a glass or like sealing member. When the cassette deforms in response to an external force, the sensor will be deformed integrally with the cassette. The prior art piezoelectric sensor, however, suffers from the drawback that the volume resistivity of the material constituting the sealing member tends to decrease in response to temperature elevation. This is reflected by a decrease in the resistance between the electrodes sandwiching the piezoelectric element therebetween and, thereby, a decrease in the output and, thereby, a decrease in the accuracy of measurement.